This invention relates generally to broadband waveguide mixers and particularly to a mixer suitable for use in the microwave and millimeter wave regions.
Various mixers have been proposed in the past for high frequency operation such as the microwave and millimeter regions. Thus in the paper to Dickens et al. which appears in the IEEE-GMTT Microwave Symposium on page 188-190 May 19, 1971, there is disclosed a mixer which operates in the microwave region which extends roughly from 1 - 300 gigahertz (GHz). The mixer is provided with back-to-back diodes mounted on a crossbar, that is on an element extending longitudinally through the structure. However the two diodes are connected in a back-to-back configuration operating as a single-ended mixer.
On the other hand, the paper to Mouw which appears in IEEE Transactions, Volume MTT-16, No. 11 November 1968, pages 911 - 918 discloses a star modulator and particularly FIG. 8a shows a doubly balanced, four diode, star mixer or modulator. This structure consists of two pairs of back-to-back diodes, each pair having a polarity opposite to that of the other pair. However, the input connections to this star mixer are rather complicated and the proposed hybrid junction is not easily adapted for millimeter wave operation. The patent to Mouw U.S. Pat. No. 3,512,090 discloses the same type of four star mixer, see for example FIG. 6.
Concerning the patented art, reference is made to the patent to Saad U.S. Pat. No. 3,532,989. The mixer shown in FIG. 2 does not have the convenient crossbar structure and requires three hybrids for its inputs. In addition the structure does not operate in the gigahertz region. A similar mixer is disclosed in the patent to Tenenholtz U.S. Pat. No. 3,706,042.
The patent to Gawler U.S. Pat. No. 3,665,508 discloses a balanced diode mixer which, however, requires more than two input transformers. Also, the structure is not adapted for the microwave region. The patent to Walsh, Jr. U.S. Pat. No. 3,553,584 relates to an up-converter and modulator for relatively low frequency applications. For the up converter of FIG. 6, only one diode is required and the pairs of diodes of FIG. 4 do not have reverse polarity. Finally, the patents to Spacek U.S. Pat. Nos. 3,584,306 and 3,638,126 both relate to high frequency converters having a crossbar but only a single pair of diodes which are connected in series.